The present invention relates to an improved flat panel display. More particularly, the present invention relates to an improved flat panel display such as a field emission display and a black matrix which improves image quality of the flat panel display.
Cathode ray tube (CRT) displays, such as those commonly used in desk-top computer screens, function as a result of a scanning electron beam from an electron gun impinging on phosphors of a relatively distant screen. The electrons increase the energy level of dopant(s) in the phosphors. When the dopant(s) return to their normal energy level, they release energy from the electrons as photons of light, which is transmitted through the glass screen of the display to the viewer.
One major disadvantage with CRT displays is that the CRT screen must be spaced from the electron gun by a relatively long distance. Moreover, CRTs typically consume relatively large amounts of power in operation. Thus, a CRT is not suited for use in small, portable devices—particularly those which operate under battery power.
Flat panel display technology is becoming increasingly important in appliances requiring lightweight portable screens. Currently, such screens typically use electroluminescent, liquid crystal, or plasma display technologies. Field emission devices represent a promising flat panel display technology which utilizes an array of cold cathodes or field emitter tips to excite pixels of phosphors on a screen. As an example, a field emission display may utilize a matrix-addressable array of cold cathodes which is selectively operated to activate particular picture segments. Field emission displays seek to combine the advantages of cathodoluminescent-phosphor technology with integrated circuit technology to create thin, high resolution displays wherein each pixel is activated by its own electron emitter.
Field emission devices generally include a baseplate assembly and an opposed faceplate. The faceplate has a cathodoluminescent phosphor coating that receives a patterned electron bombardment from the opposing baseplate, thereby providing a light image which can be seen by a viewer. The faceplate is separated from the baseplate by a vacuum gap, and outside atmospheric pressure is prevented from collapsing the two plates together by support columns. These support columns are often referred to as spacers. Arrays of electron emission sites (emitters) typically include a plurality of sharp cones that produce electron emission in the presence of an intense electric field. In the case of most field emission displays, a positive voltage is applied to an extraction grid relative to the sharp emitters to provide the intense electric field required for generating cold cathode electron emissions. Typically, FEDs are operated at anode voltages well below those of conventional CRTs.
The faceplate of a field emission display operates on the principle of cathodoluminescent emission of light. A color image can be obtained using a color sequential approach sometimes referred to as spatial integration. Nearly all commercially successful color displays today employ spatial integration to provide a color image to the viewer. A common way to employ spatial integration is to provide red, green, and blue pixels which are addressed in the form of R/G/B triads. The intensity of each of the color dots within the triad is adjusted relative to one another to produce a range of colors within the triangular boundary formed by the color coordinates of the R, G, and B dots as depicted on the 1931 or 1976 C.I.E. chromaticity diagram. During viewing, the human eye integrates the spatially separated R/G/B dots into a perceived color image.
Spatial color displays may include a dark region separating the red, green, and blue patterned dots. For optimal performance, this region should be black. A major advantage of this region, referred to as the black matrix (although not necessarily black), is improved contrast of the display in ambient light. When a black matrix is employed on the faceplate it absorbs ambient incident light, thereby improving the contrast performance of the display. The use of a black matrix or “grille” in a CRT is described, for example, in U.S. Pat. No. 4,891,110, issued Jan. 2, 1990 to Libman et al., which is hereby incorporated by reference in its entirety.
As noted above, display technology such as CRTs consumes relatively large amounts of energy. However, applications such as portable battery-operated computer displays put a premium on lower power consumption. Displays for other portable devices, such as portable stereos, electronic diaries, electronic telephone directories, and the like, also require low power consumption. Moreover, with available software features and consumer preferences, it is also desirable to provide portable devices with the ability to display color images.
Accordingly, there is a need for a flat panel color display having good contrast and reduced power consumption. Since flat panel field emission displays will become important in portable appliances that rely on portable power sources, there is a need to minimize the power consumption required by such displays. The present invention provides a field emission device which can provide color images having good contrast in a display having reduced power consumption.